- Infection of nonhuman primates with recombinant human metapneumovirus lacking the SH, G, or M2-2 protein categorizes each as a nonessential accessory protein and identifies vaccine candidates. Biacchesi, S., Pham, Q.N., Skiadopoulos, M.H., Murphy, B.R., Collins, P.L., Buchholz, U.J. J. Virol. (2005)